Recent studies
have documented an increase in the prevalence of atopic diseases in several
different parts of the world. In Brazil the prevalence of asthma, allergic rhinitis
and atopic eczema were recorded for the first time as part of an international
study and were found to be, on average, 21%, 39% and 8% respectively.1-3
These diseases often have onset in early childhood and etiologic diagnosis is
not always easy to perform. The presence of allergen-specific IgE antibodies
in serum characterizes allergic etiology. These antibodies can be detected by
in vivo testing or by biological in vitro tests.

Immediate hypersensitivity
skin tests are the weapon that has been most often used to identify specific
IgE in vivo in serum. The choice of allergens to be tested for should
be guided by anamnesis and those that are most relevant to a given region should
make up a standard battery. Previous studies, performed in varying locations
around Brazil, point to the domestic mites Dermatophagoides pteronyssinus,
Dermatophagoides farinae and Blomia tropicalis as the principal
etiologic agents of respiratory allergies.4-7 In the south of the
country, pollen has also been identified as significant.8,9

While they are
easy to perform, immediate hypersensitivity skin tests are not risk-free and
their results can suffer interference from a number of different factors. In
infants, cutaneous allergic inflammatory responses are reduced,10
making a larger proportion of false-negative results possible.

Tests performed
in vitro attempt to identify specific IgE in patients' serum and as such
require a substrate in which this immunoglobulin can be fixed for quantifying.
Questions could also be raised as to whether, produced abroad, they are relevant
in our country. Nevertheless, the allergen epitopes employed are universal and
therefore used in all countries. This study assessed the presence of serum IgE
specific to inhalant and food allergens in a population of Brazilian children
treated at allergy centers in different parts of the country.

Patients and
methods

Four hundred and
fifty-seven children participated in the study (177 girls [38.7%] and
280 boys [61.3%]) aged between 12 and 144 months, treated at allergy
centers in all five of Brazil's regions. The children were classed into five
age groups as follows: 1 to 2 years, 2 to 3 years, 3 to 4 years, 4 to 5 years
and 5 to 12 years. Children were classed as atopic if they presented at least
one positive immediate hypersensitivity skin test (mean wheal diameter greater
than or equal to 3 mm)10,11 to at least one inhalant or food allergen,
tested randomly at the patient's allergy center of origin. The control group
was made up of 62 other children recruited from the investigation centers in
the Northeast, Southeast and South regions with no history of allergic disease
and negative immediate hypersensitivity skin tests results for the same allergens
used at the centers they came from and who had required blood testing for other
reasons such as preoperative assessments for elective surgery.10,11

Depending on the
reason for referral, patients were classed as: wheezing infants (n = 20), food
allergy (n = 16), atopic dermatitis (n = 56), and respiratory allergy (n = 348).
Babies were defined as wheezing if they were less than two years old and presented
recurrent episodes of wheezing and other possible causes had been ruled out
(aspiration syndromes, fibrocystic disease, airway malformations among others).
Patients with proven asthma and/or rhinitis were defined as having respiratory
allergies.

Peripheral blood
samples were taken from both allergic and control patients so that IgE serum
levels specific to inhalant allergens (Dermatophagoides pteronyssinus,
Dermatophagoides farinae, Blomia tropicalis, cat, dog, molds,
cow's epithelium, horse, grasses and cockroach) and food allergens (cow's milk,
egg, peanut, wheat and seafood panel) and total IgE serum levels (UNiCAP®-Pharmacia)
could be assayed.12,13 Specific IgE levels (RAST) greater than or
equal to 0.35 UI/ml (class 1) were defined as positive13,14 The study
was approved by the relevant Ethics Committees and free and informed consent
was obtained.

Non-parametric
tests were employed to analyze variables and in all cases the cut off for null
hypothesis rejection was set at 5%.

Results

Observing Table
1 we find the distribution of allergic patients. As will be noted, distribution
was even in terms of age groups and region of origin. The same was true of sex
(data not shown). Controls were limited to the Northeast, Southeast and South
regions because there were less of them and also exhibited no differences in
terms of age group: less than 2 years old = 19.4%; 2 to 3 years = 20.9%; between
3 and 4 years = 14.5%; between 4 and 5 years =20.9% and between 5 and 12 years
= 24.2%.

The presence of
specific IgE to inhalant and/or food allergens was variable, being significantly
less common among younger allergic patients (Table
2). There were no differences observed between patients with negative RAST
results and non-allergic controls (Table
2).

Total IgE serum
levels vary greatly and because of this they are expressed as geometric means.
Levels were significantly more elevated among atopic subjects when compared
to controls and increased with age (Table
3 and Figure 1). When the presence or absence of IgE
specific to any of the tested allergens was analyzed among the atopic patients,
it was found that, for all age groups, those that were RAST positive (R+) also
had significantly more elevated total IgE values than those who were RAST negative.
The same was true when R+ subjects were compared with controls (Table
3 and Figure 1). Comparative analysis of the controls
and the RAST negative atopic children did not reveal any significant differences
with the exception of the 4-5 year age group (Table
3 e Figure 1).

Serum IgE specific
to inhalant and/or food allergens tests were positive for 361/457 (79%) of the
patients and 16/62 (28.8%) of the controls. Table
4 contains the frequency of each result according to allergen tested. It
shows that inhalant allergens, in particular mites, were most prevalent. In
the food category fish, egg, cow's milk and wheat stand out (Table
4). Table 5 shows the
frequency of positive results for each of the allergens tested by age group
and taking the total number of positive results for each particular allergen
as a reference. Significantly lower frequencies will be observed among younger
children. There were no differences in terms of IgE specific to cat, cow's epithelium,
dog, horse or molds (Table 5).
Of all the foods, sensitization to the seafood panel was most frequent, being
lower among the younger subjects. There was a high frequency of sensitization
to cow's milk across all age groups (Table
5). Ninety-six patients were found to be exclusively sensitized to either
food or inhalant allergens (Table 6). Comparing the two
groups, we found that sensitization to foods predominated for the first few
years and sensitization to inhalants in later age groups.

We found different
levels of positivity to tested allergens according to the primary complaint
leading to observation (Table 7). Children with respiratory
allergies and atopic dermatitis had a greater frequency of positivity to inhalant
allergens. Nevertheless, 38.8% of those with respiratory allergies were sensitized
to fish. A lower proportion was observed among those with atopic dermatitis.
Children with food allergies were more frequently sensitized to cow's milk,
egg, wheat, fish and soya. Despite this, the group also recorded a significant
level of sensitization to domestic dust mites and, in particular, cow's epithelium
(Table 7). A lower prevalence of sensitization was observed
among the wheezing infants with a predominance of inhalant allergens (mites
and cow's epithelium).

Sensitization to
more than one allergen was observed in 85% of the patients, particularly among
the oldest. The most frequently encountered combinations were the three types
of mite, cow's milk with cow's epithelium and mites, cockroaches and fish all
three concomitantly. There were no differences in the pattern of sensitization
distribution by patient region of origin (data not shown).

Discussion

Elevated IgE serum
levels have been hailed as markers for atopic disease. However, a number of
different clinical circumstances, in addition to allergic diseases, may progress
with elevated total IgE serum levels, for example intestinal helminthiasis and
an active smoking habit. Prospective studies in which total IgE was measured
in cord blood allowed increased risk for the development of asthma and allergic
diseases to be detected in newborn babies with levels above 0.9UI/ml.15
In a previous study that attempted to establish normal total IgE serum values,
Mancini et al. recorded total IgE values below 1.0 UI/ml, in cord blood. However,
in older children levels were observed to increase with age and become greatly
divergent which meant that the production of a national standard for IgE serum
levels was not viable.16

Lopez et al. studied
the relationship between total IgE serum levels and early wheezing in infants
followed for the first year of life.17 They found higher levels of
total IgE in the cord blood of those that would later wheeze, but the difference
was not significant. The newborn babies were monitored and there was a significant
increase in IgE serum levels as they got older. At 12 months there was also
specific sensitization to egg white (43%), cow's milk (60%) and, to a lesser
degree, to D.pteronyssinus (30%) and D. farinae (33%).17

In the current
study total IgE serum levels in the control group exhibited a tendency towards
more elevated values in older children. Values in the atopic group were significantly
higher for all age groups, with significant increases with age (Table
3 and Figure 1). One interesting fact was that when
the atopic group was divided by the presence of at least one R+, we found that
children with negative results presented values significantly lower than those
with R+ and a little higher than the controls.

In addition to
genetic potential, environmental exposure to allergens is fundamental to atopic
sensitization and disease expression. Longitudinal studies of wheezing infants
point to the presence of serum IgE specific to inhalant allergens as an indicator
of high risk for the development of asthma when school age.18 In
children less than two years old hospitalized for wheezing, the presence of
R+ for wheat, egg white and domestic dust mites was associated with an increased
frequency of asthma later in life.19 Despite this, specific IgE serum
assay is not an available test at the majority of health care services, whether
governmental or private.

When assessing
allergic patients it is important to bear the concept of the allergic march
in mind. It is known that allergic manifestations progress from atopic eczema
and food allergies in younger children to respiratory allergy later on, manifesting
as asthma and rhinoconjunctivitis.20 This fact was taken into account
for the present study. Despite a predominance of children from the Southeast
region of Brazil, the distribution according to age group was comparable for
all regions

Taking the sample
as a whole, we observed an accentuated predominance by inhalant allergens, in
particular the mites D. pteronyssinus (67.8%), D. farinae (66.5%)
and Blomia tropicalis (57.1%) and cockroach allergens (34.4%). This data
is explained by the fact that 348/457 (76.1%) of the patients were being monitored
because of respiratory allergy. Previous studies in our country have already
isolated these mites as having the greatest sensitization prevalence.4-7

One further fact
that attracted our attention was the elevated rate of sensitization to domestic
mites observed among patients suffering from atopic dermatitis (AD). A longitudinal
study on secondary prophylaxis for asthma found that 17% of the European children
with AD being studied were sensitized to domestic dust mites and 10% to pollen.21
Furthermore, the reduction in DA symptom scores after measures had been
taken to reduce exposure to domestic dust mites, in particular from mattresses,
together with the development of asthma by around 50% of DA patients22
reinforces the evidence for the participation of mites as important etiologic
agents of DA.

Among patients
with clinical history of food allergies there was a predominance of sensitization
to aeroallergens, albeit in smaller proportions. Cow's milk was the most often
identified food allergen followed by egg white, wheat, fish and soya (Table
7). In general cow's milk proteins are the first heterologous dietary proteins
with which infants come into contact, which explains early sensitization.23
Within this population we observed a predominance of sensitization to cow's
milk among children less than two years old and sensitization to fish occurred
among older children, bearing in mind that the introduction of this element
into the diet generally occurs after one year of life. We did not detect any
differences in sensitization prevalence to the different allergens according
to patient region of origin.

Around 15% of
the patients assessed were mono-sensitized. Food allergen sensitization was
more prevalence among the younger subjects. Aeroallergens predominated among
older children (Table 6). Insidious exposure to small quantities
of aeroallergens may be the explanation for the delay in aeroallergen sensitization.20
A prospective study of children, from birth to six years old, recorded a fall
in sensitization to food allergies from 10% during the first year to 3% at six.
The opposite behavior was observed in relation to inhalant allergens which,
from 1.5%, reached 8% at six years.24 The current study was not prospective
and as such it was not possible to study this type of behavior.

The presence of
serum IgE specific to inhalant and/or food allergens was significantly greater
among the atopic subjects and was related to age, oscillating between 63.6%
for those less than 24 months old to 98.2% for those over 60 months old. While
there were positive results in the control group, IgE levels were lower and
reached a maximum of 37.5% of positive exams. Table
4 lists the frequency of positivity to the allergens tested. There was a
predominance of inhalant allergens (D. pteronyssinus, D. farinae,
Blomia tropicalis and cockroach) over food allergens (fish, egg, cow's
milk and wheat). The same occurred with the control group although in less significant
proportions (Tables 4 and
5).

The battery of
allergens employed for the immediate hypersensitivity skin tests were not standardized
in terms of their origin. This being the case it was not possible to study agreement
between the skin tests and the specific IgE tests.

Within the population
under study, only 15% exhibited sensitization to just a single allergen. Among
the remaining patients we observed frequent concomitant sensitization combinations
of all three mites or all three mites and cockroach, to the preceding four and
the seafood panel. The existence of cross-reactivity between these allergens
is the most plausible explanation. The all have tropomyosin in common, which
is a contractile protein present in the mites, cockroaches and seafood (shrimps).25
Another combination of positive results was cow's milk with cow's epithelium.
Could the presence of bovine serum albumin the main cause of their cross-reactivity?
This question should be researched.

In conclusion,
this is the first national Brazilian study that has assessed the pattern of
sensitization to inhalant and food allergens in atopic children. It has identified
a similar pattern of sensitization in all regions of the country. For patients
with respiratory symptoms a panel composed of domestic dust mites, possibly
with cat or dog allergens added can aid in the identification of sensitized
individuals. When patients have food allergies, a panel made up of cow's milk,
wheat, fish, egg white and soya allergens can be of assistance.

Acknowledgements

We would like
to thank Mr. Fábio Arcuri (Pharmacia do Brasil) for donating the
test kits and to Doctors Paulo G Leser and Roseli Dobner dos Santos at the Laboratório
Fleury for performing experiments and to the other members of the PROAL
Group for data collection.

21. ETAC Study Group. Allergic factors associated with the development of asthma and the influence of cetirizine in a double-blind, randomized, placebo-controlled trial: first results of ETAC. Pediatr Allergy Immunol. 1998;9:116-24. [ Links ]